Single-zone rooftop units have been used worldwide for the last 40 years on small office buildings, shopping malls, and retail stores. Single-zone air conditioning units have long been the lowest first-cost method of air conditioning buildings. The operating cost (energy use) of the systems has not been a significant consideration until recently, with the current focus on energy consumption and its link to both global warming and increased costs.
As air conditioning units go, single-zone package units have been considered to be a commodity item and, as such, they have limited sophistication when it comes to energy saving features. Current state-of-the-art air conditioning units are becoming more energy efficient by using variable airflow, improved heat transfer surfaces, more efficient fans, and more efficient compressors, but no retrofit exists for the literally millions of existing air conditioning units that could operate with less energy without sacrificing comfort. A retrofit is needed that may be applied to any brand of rooftop unit with gas, electric, or reverse cycle (heat pump) heat.